The compound 1-(4-amino-6,7-dimethoxy-2-quinazolinyl)-4-(tetrahydro-2-furoyl)piperazine is internationally known under the name of terazosin.
This compound, together with the anhydrous monohydrochloride salt, has been described for the first time in U.S. Pat. No. 4,026,894.
In the subsequent U.S. Pat. No. 4,251,532 a crystalline dihydrate form of terazosin has been described defined more stable than the original anhydrous form. This dihydrate form of the terazosin monohydrochloride is at present marketed all over the world, for instance as HYTRIN.RTM. in USA and United Kingdom and as ITRIN.RTM. in Italy, for the treatment of the hypertension.
Recently U.S. Pat. No. 5,412,095 has described and claimed new crystalline forms of the terazosin monohydrochloride anhydrous, named FORM II and FORM III, and a new process for producing the original anhydrous monohydrochloride crystalline form described in U.S. Pat. No. 4,026,894 named "a posteriori" FORM I.